Methods to Eliminate High Pressure Surges in HVAC Systems

ABSTRACT

A system and method are disclosed for relieving high pressure within an HVAC system. A bypass line is provided that can direct refrigerant away from an expansion device within the HVAC system. The bypass line then returns the refrigerant to the HVAC system. Other locations of bypass lines can be used as well. A controller for the HVAC system can control access to the bypass line and measure pressure within the system.

TECHNICAL FIELD

The present disclosure is directed to HVAC systems and more particularlyto pressure relief for these systems.

BACKGROUND OF THE INVENTION

HVAC systems may have pressure sensitivities during operation. Forexample, air conditioners may include microchannel condensers (e.g.,condenser with a channel size less than approximately 1 mm) rather thanother types of condensers (e.g., condenser with tube size greater than 5mm). The buildup of refrigerant pressure in HVAC systems is a commonproblem. The problem can be particularly acute in systems with amicrochannel condenser because microchannel condensers may be sensitiveto certain operating conditions. For example, when ambient temperatures(e.g., temperatures proximate a condenser or temperature proximate acondenser fan) are high, the pressure in the microchannel condenser maybecome elevated due to the refrigerant capacity size difference betweenthe microchannel condenser and the evaporator. The high pressures (e.g.,pressures greater than approximately 615 psi, in some embodiments) maycause mechanical failure, including prefailure events, such as excessivewear on parts. High pressures may also trip safety systems designed toprevent overpressure. One previous solution has been to limitrefrigerant within an HVAC system. However, this solution leads to aloss in cooling capacity or efficiency.

A particular problem can occur upon startup of an HVAC system.Refrigerant may not be evenly/properly distributed within the system,leading to refrigerant and/or pressure imbalances. One solution has beento change the size of microchannels within the HVAC system, such as inthe condenser. However, this may limit other properties or capabilitiesof the system, and such a solution may not be feasible as a retrofitsolution.

BRIEF SUMMARY OF THE INVENTION

One embodiment of the present disclosure is an HVAC system comprising anevaporator operable to receive refrigerant in a liquid state andevaporate the refrigerant into a gaseous state; a pressure sensor, thepressure sensor located within a liquid line of the HVAC system andoperable to measure the pressure within the liquid line; a compressoroperable to receive refrigerant from the evaporator; a condenseroperable to receive refrigerant from the compressor in a gaseous stateand condense the refrigerant into a liquid state; an expansion deviceoperable to receive refrigerant from the condenser and direct therefrigerant toward the evaporator; a bypass line, the bypass lineoperable to direct refrigerant away from the expansion device and returnthe refrigerant to the HVAC system; and a controller, the controllercoupled to at least the pressure sensor and the bypass line, thecontroller operable to direct refrigerant to the bypass line when thepressure reaches a predetermined value.

Another embodiment comprises a method of relieving pressure within anHVAC system comprising: receiving a signal to start the HVAC system;opening a bypass line, the bypass line capable of diverting refrigerantaway from an expansion valve and returning the refrigerant to the HVACsystem; starting the HVAC system; and closing the bypass line when apredetermined event has occurred.

Another embodiment comprises a method of operating an HVAC systemcomprising a controller, a condenser, a compressor, an evaporator, andan expansion device, the method comprising: receiving, at thecontroller, a pressure reading for the HVAC system; opening, by thecontroller, a valve to a bypass line when the pressure reading exceeds apredetermined value; wherein the bypass line directs refrigerant awayfrom an expansion device and returns the refrigerant to the HVAC system.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims. The novel features which are believed to be characteristic ofthe invention, both as to its organization and method of operation,together with further objects and advantages will be better understoodfrom the following description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following descriptions taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a diagram of a system embodiment of the present disclosure.

FIG. 2 is a diagram of an alternative system embodiment of the presentdisclosure.

FIG. 3 is a diagram of an alternative system embodiment of the presentdisclosure.

FIG. 4 is a flow-chart diagram of a method embodiment of the presentdisclosure.

FIG. 5 is a flow-chart diagram of an alternative method embodiment ofthe present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

HVAC systems may have pressure sensitivities (surges) during operation.For example, air conditioners may include microchannel condensers (e.g.,condenser with a channel size less than approximately 1 mm) rather thanother types of condensers (e.g., condenser with tube size greater than 5mm). Microchannel condensers may be sensitive to certain operatingconditions, especially the pressure at the compressor discharge. Forexample, when ambient temperatures (e.g., temperatures proximate acondenser or temperature proximate a condenser fans) are high, thepressure in the microchannel condenser may become elevated due to therefrigerant capacity size difference between the microchannel condenserand the evaporator. The high pressures (e.g., pressures greater thanapproximately 615 psi, in some embodiments) may cause mechanicalfailure, including prefailure events, such as excessive wear on parts.High pressures may also trip safety systems designed to preventoverpressure. If air conditioner operation is allowed when the pressureexceeds a predetermined operational maximum (e.g., greater thanapproximately 615 psig and/or greater than approximately 620 psig forR410A, in some embodiments), mechanical failure events may occur. Forexample, mechanical failure events, including pre-failure events, mayinclude wear on parts, damage to lines, damage to seals, and/or damageto components. Startup of HVAC systems can provide unique pressureproblems as well. HVAC systems may have startup problems withmicrochannel condensers because of the refrigerant storage imbalancebetween a microchannel condenser and round tube flat fin coilevaporators. If the microchannel tube port size is too small, the HVACsystem start up problem may be elevated. Various condenser andevaporator types and geometries can cause pressure spike or buildupproblems.

Embodiments of an HVAC system as described in the present disclosure canprovide a system and method for relieving pressure buildup within anHVAC system, during operation or upon startup. The present disclosurecan be adapted to various condenser, evaporator and HVAC system types.

In a typical prior art system, refrigerant passes through an evaporator,pulling heat from surrounding air, and evaporating the refrigerant togas form. Then the gas can be compressed in a compressor before passingthrough a condenser. As gas refrigerant passes through a condenser itloses heat to the surrounding air, leaving the refrigerant again inliquid form. The refrigerant then flows through an expansion device tothe evaporator. In some embodiments, the evaporator is located within aroom or building, creating a cooling effect (an air conditioner). Otherembodiments may place the condenser inside a room or building, creatinga warming effect (a heat pump).

Referring to FIG. 1, an embodiment of the present disclosure can beseen. System 10 is an HVAC system comprising a microchannel condenser40, a compressor 30, an evaporator 20, distributor 70, expansion device50, solenoid valves 55 and 65. Pressure imbalances or pressure spikescan be common when first starting up an HVAC system such as system 10.To relieve the pressure upon startup, solenoid valve 55 can be opened,causing some or all refrigerant to bypass the expansion device 50 byusing bypass line 58. As the refrigerant is allowed to pass through agreater area of pipe the pressure within the condenser 40 and the otherportion with high pressure in the system is reduced. Other types ofvalves can be used instead of solenoid valves 55. In some embodimentsexpansion device 50 may also comprise a metering device. Solenoid valves55 and/or 65 can be replaced by, or comprise, a pressure regulatingvalve 65. Valve 65 can also be used to bypass condenser 40 by openingbypass line 68. Elements 65, 50, 55 may also comprise pressure sensorsto help measure pressure within the system. When pressure readings arehigh this may trigger, for example, valve 65 to open. Elements 30, 40,20 and 70 could also comprise pressure sensors in some embodiments. Acontroller (not shown) may connect to all these components and anyavailable pressure sensors, and can receive measurements and adjustvalves or other components accordingly.

The embodiment shown in FIG. 1 uses a bypass line 58 with a shut offsolenoid valve 55 to bypass expansion device 50. The solenoid valve 55can remain open when the unit is started and will be shut off within afew minutes after startup of the system. The exact time required to shutoff the solenoid valve 55 may vary for different HVAC systems. The shutoff solenoid valve 55 can be also controlled by the signal of compressordischarge pressure. For example, if the compressor discharge pressure isclose to the high pressure switch setting pressure, the solenoid valve55 will be open a short time as required to prevent high pressure switchtripping off. If the high pressure surge is still high enough to tripoff the high pressure switch valve, a hot gas bypass 68 from the outletof compressor 30 to the inlet of the evaporator 20 may be necessary. Apressure regulating valve 65 can be used in the hot gas bypass 68 sothat the compressor discharge pressure cannot be reached to trip off thehigh pressure switch. An alternative way for the hot gas bypass 68 is touse a solenoid valve to control the hot gas bypass 68. If the compressordischarge pressure reaches close to the high pressure switch trip offpressure, the solenoid valve in the hot gas bypass 68 will be open for arequired short period of time to release the compressor dischargepressure (i.e. the pressure at compressor discharge).

FIG. 2 displays an alternative embodiment of the present disclosure.HVAC system 100 comprises an evaporator 120, compressor 130, condenser140, expansion valve 150, valve 155, and distributor 170. A plurality ofpressure sensors can be located at various locations within system 100,including at any of the numbered elements. A controller (not shown) maybe connected (wired or wirelessly) with a plurality of pressure sensorsand/or the other components. The controller can thereby monitor thepressure of the system and adjust valves and other componentsaccordingly. As shown in FIG. 2, if there is a pressure spike, the valve155 (possibly a solenoid valve and/or a pressure regulating valve, oranother type of valve) may open, diverting at least some refrigerantfrom expansion device 150 and relieving the system 100 from highpressure.

In some implementations, the condenser may be a microchannel condenser.A microchannel condenser may include channels less than approximately 1mm. The channels of the microchannel condenser may have across-sectional area similar to a rectangle, an oval, and/or any otherappropriate shape. A microchannel condenser may increase the efficiencyand/or decrease energy consumption of an air conditioner (e.g., whencompared to an air conditioner with a condenser with a tubing diametergreater than 5 mm). A microchannel condenser may be able to operate withless refrigerant (e.g., when compared to an air conditioner with acondenser with a tubing diameter greater than 5 mm).

In some implementations, a part of the refrigerant may flow through thebypass line (elements 68, 58, 158 from FIGS. 1 and 2). For example, lessthan 50 percent of the refrigerant in a line (e.g., a line from the highpressure portion) may be allowed to flow through the bypass line. Insome implementations, approximately 5 to approximately 10 percent of therefrigerant may be allowed to flow through the bypass line. Less than 20percent of the refrigerant in a line may be diverted to flow through thebypass line in some implementations. In some implementations, the amountof refrigerant allowed to flow through the bypass line may be at leastpartially based on a size of the bypass line (e.g., absolute size and/orsize of the bypass line compared to other lines in the air conditioningsystem). The size (e.g., diameter and/or cross-sectional area) of thebypass line may be selected to allow a predetermined amount ofrefrigerant to flow through the bypass line.

FIG. 3 shows an embodiment with pressure sensors 256, 266 coupled tovalves 255, 265 on the bypass lines 258, 268 that may control the amountof refrigerant allowed to pass through the bypass line 258, 268. Thevalves 255, 265 may be disposed in the bypass line 258, 268. A sensor256, 266 may be coupled to the valve 255, 265 and/or operations of thevalve 255, 265 may be based at least partially based on the propertyreading from the sensors 256, 266. For example, the valves 255, 265 mayopen when a property reading exceeds a predetermined maximum property.The valves 255, 265 may close at other times. For example, a valve 255,265 may automatically close and restrict flow through the bypass lines258, 268 when a property reading does not exceed a predetermined maximumproperty. In some implementations, the valves 255, 265 may automaticallyoperate based on the property reading. FIG. 3 also shows a controller280 coupled to the valves 255, 265, sensors 256, 266 and other elementsof system 200. The controller 280 may control the openness of the valves255, 265 to control the amount of refrigerant allowed to pass throughthe bypass lines 258, 268. The controller may include a computer and/orother programmable logic device. The controller may comprise aninterface for use by a user. Alternatively a user interface may comprisea separate component in communication with the controller. Valve 255 andsensor 256 may be set for different pressure measurements (or otherproperties) than valve 265 and sensor 266, so the two bypass lines mayfunction independently of one another.

The sensors 256, 266 may detect other properties of the air conditioningsystem 200. For example, the sensor 256, 266 may detect properties suchas temperature, pressure, and/or other appropriate properties. Thesensor 256, 266 may detect the property at various positions in linesand/or components of the air conditioning system. For example, thesensors 256, 266 may detect a property (e.g., temperature and/orpressure) such as an ambient temperature (e.g., a temperature proximatethe condenser). The sensors 256, 266 may also be disposed at a pluralityof other locations within system 200.

In keeping with the teachings of the present disclosure, a high pressureswitch can be located at any suitable location within an HVAC system.For example, the high pressure switch may be disposed proximate anoutlet of the compressor, and/or proximate an outlet of the condenser.

In some implementations, when the air conditioner includes a condenserthat it not a microchannel condenser, high pressures (e.g., greater thanpredetermined maximum and/or predetermined operational maximum) may notoccur (e.g., during high ambient temperature operations) due to thesmaller capacity difference between the condenser and the evaporator(e.g., when compared to the capacity difference between a microchannelcondensers and an evaporator). But the teachings of the presentdisclosure can still be used for non-microchannel implementations.

FIG. 4 illustrates an implementation of an example process 400 for anoperation of an air conditioning system. An HVAC system is providedcomprising an evaporator, compressor, condenser and expansion device410. A bypass line is provided that is capable of diverting refrigerantaway from the expansion device 420. Pressure is measured within the HVACsystem 430. The bypass line is opened when the pressure reaches apredetermined limit 440. For example, a sensor positioned in at least aportion of the air conditioner may measure a property (e.g.,temperature, pressure, temperature differential, and/or pressuredifferential, such as a pressure difference over time or a pressuredifference between two points in the system) of the air conditioner. Thesensor may be a portion of a control device (e.g., such as a smart valveand/or air conditioner controller).

FIG. 5 illustrates another method embodiment 500 of the presentdisclosure. At a controller for an HVAC system a pressure reading isreceived 510. Then the controller opens a valve to a bypass line whenthe pressure reading exceeds a predetermined value 520. The bypass linedirects refrigerant away from an expansion device and returns therefrigerant to the HVAC system. The bypass line may be closed at a latertime such as when an event occurs. Possible trigger events can include atimer (passing of a predetermined time period), pressure dropping belowa chosen level, or another event.

If the pressure reading exceeds a predetermined maximum, flow throughthe bypass line may be allowed. For example, the controller may transmita signal to a valve disposed in the bypass line. The valve may at leastpartially open if the property reading exceeds the predetermined maximumproperty. In some implementations, the amount of refrigerant allowed toflow through the bypass line may be based at least partially on thedegree of openness of the valve. The amount of refrigerant allowed toflow through the bypass line may be based on the size of the bypassline. Allowing fluid flow through the bypass line may reduce a pressureof at least a part of the high pressure portion of the air conditioner.If the property reading does not exceed the predetermined maximumproperty, flow through the bypass line may be restricted. For example, avalve disposed in the bypass line may be closed if the property readingis does not exceed the predetermined maximum property.

A determination may be made whether a pressure reading exceeds apredetermined maximum pressure reading. For example, a predeterminedmaximum pressure reading may be retrieved from a memory of the airconditioner and/or controller. The pressure reading and thepredetermined reading may be compared (e.g., by a processor of thecontroller of the air conditioner, by a valve controller, and/or by thesensor). In some implementations, the pressure reading may be a pressuredifferential across the compressor and the predetermined maximumpressure differential across the compressor may be 460 psi for R410A.The pressure reading may be an absolute pressure and the predeterminedmaximum pressure may be 600 psig. For example, a pressure of refrigerantin a line may be a measured pressure reading and the associatedpredetermined maximum pressure reading may be 600 psig. In someimplementations, the predetermined maximum pressure may be a preselectedamount (e.g., 10 psi, 15 psi, and/or 20 psi) less than the maximumoperational pressure (e.g., the pressure at which a high pressure switchrestricts operation of at least a portion of the air conditioning systemto inhibit mechanical failure of the system). The predetermined maximumpressure may be selected such that operation of the high pressure switchmay be avoided when using the bypass line.

In some implementations, in an air conditioner that includes amicrochannel condenser, as the ambient temperature becomes elevated(e.g., ambient temperatures greater than 125 degrees Fahrenheit and/or116 degrees Fahrenheit), the pressure in the microchannel condenserincreases (e.g., due to the capacity differences between the evaporatorand the microchannel condenser). A sensor can be disposed proximate atleast a portion of the condenser and may measure the pressure (e.g.,pressure reading). As the pressure (e.g., inlet, outlet, differential,and/or average) of the microchannel increases, the likelihood ofmechanical failure increases, and so a high pressure switch may operateat a predetermined activation pressure (e.g., a maximum operationalpressure) to inhibit mechanical failure of the air conditioner. Forexample, the high pressure switch may restrict operation of one or morecomponents of the air conditioner (e.g., compressor) and/or open a vent.The predetermined maximum pressure may be determined based on the highpressure switch activation pressure, in some implementations. Forexample, the predetermined maximum pressure may be a predeterminedamount less than the maximum operational pressure (e.g., thepredetermined maximum pressure may be approximately 15 to approximately20 psi less than the predetermined maximum operational pressure). Themeasured pressure may be compared to the predetermined maximum pressureto determine whether to allow a part of the refrigerant to be divertedto the bypass line. When the measured pressure exceeds the predeterminedmaximum pressure, a valve coupled to the sensor may open and allowrefrigerant to flow through the bypass line. The bypass may reduce thepressure and/or inhibit pressures in the microchannel condenser fromelevating to the activation pressure. When the measured pressure doesnot exceed the predetermined maximum pressure, fluid flow through thebypass line may be restricted (e.g., by the valve coupled to thesensor). For example, the bypass line may be utilized to reduce thepressure, when needed to control pressure in the microchannel condenserand/or to inhibit mechanical failure. When the pressure of themicrochannel condenser is within operational parameters (e.g., less thanthe predetermined maximum pressure and/or predetermined maximumoperational pressure), the fluid flow through the bypass line may berestricted to increase efficiency of the system and/or control ofpressure within the evaporator.

Although various implementations have been described in terms ofpressure and pressure sensors, other properties may be utilized in thevarious systems and/or processes. For example, a temperature sensor maybe utilized. Temperatures, such as ambient temperature may be measuredby sensors and the valve in the bypass line may operate based on themeasured temperature. Although a valve coupled to the bypass line thatopens to allow fluid flow through the bypass line has been described,other valve configurations may be allowed as appropriate. For example, athree way valve coupled to the junction between the bypass line and thehigh pressure portion and/or low pressure portion, may direct fluidflow.

In some implementations, ambient temperature may include a temperatureproximate the high pressure portion, a temperature proximate thecondenser, and/or a temperature proximate a condenser fan. For example,ambient temperature may include a measure of the temperature of the airproximate an outdoor portion (e.g., a condenser) of an air conditioningsystem. As another example, ambient temperature may include a measure ofthe temperature of a fluid removing heat from the refrigerant in thecondenser. Temperature measurements may cause an adjustment to themaximum allowed pressure, depending on the properties of the refrigerantused, or other factors.

In some implementations, a pressure across a line coupling componentsmay be substantially constant. For example, a pressure drop across aline coupling components may be less than approximately 5 percent. As anexample, a pressure proximate an inlet of a high pressure portion and/orcondenser may be substantially equal to the pressure proximate an outletof a compressor. A sensor measuring a pressure in a line may notsubstantially affect the pressure. In some implementations, a pressureacross the high pressure portion and/or the pressure across the lowpressure portion may be substantially constant. For example, a pressuredrop across the high pressure portion may be less than approximately 5percent. The pressure drop across the low pressure portion may be lessthan approximately 5 percent.

Although an expansion valve has been described, any appropriate meteringdevice may be utilized to control fluid flow into the evaporator. Forexample, a thermal expansion valve may be utilized.

Although an operation of the cycle is described where cool air isprovided to a location by the evaporator which is the indoor coils, thecycle may be reversed such that hot air is provided to a location by theindoor coils. For example, heat may transfer from refrigerant in theindoor coils to the air from the indoor blower.

In some implementations, the air conditioning system may include acontroller. The control device for the bypass valve may be a portion ofthe controller and/or separate from the controller. A controller may becoupled to various components of the air conditioning system. Forexample, the controller may be communicably coupled to an evaporator, anevaporator blower, a compressor, a condenser, a condenser fan, bypassline, sensor, high pressure switch, control device of the sensor, valve,and/or thermal expansion valve. The controller may be a computer orother programmable logic device. The controller may include a processorthat executes instructions and manipulates data to perform operations ofthe controller and a memory. The processor may include a programmablelogic device, a microprocessor, or any other appropriate device formanipulating information in a logical manner and memory may include anyappropriate form(s) of volatile and/or nonvolatile memory, such as arepository. A memory may include data, such as predetermined maximumoperating properties (e.g., temperatures and/or pressures), activationpressures, predetermined maximum properties (e.g., temperatures and/orpressures), periods of time that operations should run, and/or any otherdata useful to the operation of the air conditioner. In addition,various types of software may be stored on the memory. For example,instructions (e.g., operating systems and/or other types of software),an operation module, a bypass operation module, and/or a high pressureswitch module may be stored on the memory. The operation module mayoperate the air conditioner during normal operations (e.g., operationsbased at least partially on requests for operation from a user,operations in which flow though the bypass is restricted). The bypassoperation module may measure and/or monitor properties of the airconditioning system, retrieve data (e.g., predetermined operationalmaximums and/or predetermined maximum values), compare data to monitoredproperties, determine whether to open and/or close a bypass line, etc. Ahigh pressure switch module may measure and/or monitor properties, suchas pressure, retrieve data (e.g., predetermined operational maximum),compare monitored properties to retrieved data, and/or determine anappropriate action based on the retrieved data (e.g., restrict operationof one or more components of the air conditioner and/or allow normaloperations).

A communication interface may allow the controller to communicate withcomponents of the air conditioner, other repositories, and/or othercomputer systems. The communication interface may transmit data from thecontroller and/or receive data from other components, otherrepositories, and/or other computer systems via network protocols (e.g.,TCP/IP, Bluetooth, and/or Wi-Fi) and/or a bus (e.g., serial, parallel,USB, and/or FireWire).

The controller may include a presentation interface to present data to auser. For example, to provide for interaction with a user, the systemsand techniques described here can be implemented on a computer having adisplay device (e.g., a CRT (cathode ray tube) or LCD (liquid crystaldisplay) monitor) for displaying information to the user and a keyboardand a pointing device (e.g., a mouse or a track pad) by which the usercan provide input to the computer. Other kinds of devices can be used toprovide for interaction with a user as well; for example, feedbackprovided to the user by an output device can be any form of sensoryfeedback (e.g., visual feedback, auditory feedback, or tactilefeedback); and input from the user can be received in any form,including acoustic, speech, or tactile input. The controller may includeclients and servers. A client and server are generally remote from eachother and typically interact through a communication network. Therelationship of client and server arises by virtue of computer programsrunning on the respective computers and having a client-serverrelationship to each other. A client may allow a user to access thecontroller and/or instructions stored on the controller. The client maybe a computer system such as a personal computer, a laptop, a personaldigital assistant, a smart phone, or any computer system appropriate forcommunicating with the controller. These computer programs (also knownas programs, software, software applications or code) include machineinstructions for a programmable processor, and can be implemented in ahigh-level procedural and/or object-oriented programming language,and/or in assembly/machine language. As used herein, the term“machine-readable medium” refers to any computer program product,apparatus and/or device (e.g., magnetic discs, optical disks, memory,Programmable Logic Devices (PLDs)) used to provide machine instructionsand/or data to a programmable processor, including a machine-readablemedium that receives machine instructions as a machine-readable signal.The term “machine-readable signal” refers to any signal used to providemachine instructions and/or data to a programmable processor.

Although users have been described as a human, a user may be a person, agroup of people, a person or persons interacting with one or morecomputers, and/or a computer system. Various implementations of thesystems and techniques described here can be realized in digitalelectronic circuitry, integrated circuitry, specially designed ASICs(application specific integrated circuits), computer hardware, firmware,software, and/or combinations thereof. These various implementations caninclude implementation in one or more computer programs that areexecutable and/or interpretable on a programmable system including atleast one programmable processor, which may be special or generalpurpose, coupled to receive data and instructions from, and to transmitdata and instructions to a storage system (e.g., repository), at leastone input device, and at least one output device.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, compositionof matter, means, methods and steps described in the specification. Asone of ordinary skill in the art will readily appreciate from thedisclosure of the present invention, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present invention.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

What is claimed is:
 1. An HVAC system comprising: an evaporator operableto receive refrigerant in a liquid or two-phase state and evaporate therefrigerant into a gaseous state; a pressure sensor, the pressure sensorlocated within a liquid line of the HVAC system and operable to measurethe pressure within the liquid line; a compressor operable to receiverefrigerant from the evaporator; a condenser operable to receiverefrigerant from the compressor in a gaseous state and condense therefrigerant into a liquid state; an expansion device operable to receiverefrigerant from the condenser and direct the refrigerant toward theevaporator; a bypass line, the bypass line operable to directrefrigerant away from the expansion device and return the refrigerant tothe HVAC system; and a controller, the controller coupled to at leastthe pressure sensor and the bypass line, the controller operable todirect refrigerant to the bypass line when the pressure reaches apredetermined value.
 2. The HVAC system of claim 1 wherein the condensercomprises a microchannel condenser.
 3. The HVAC system of claim 1further comprising a second bypass line, the second bypass line operableto direct refrigerant away from the microchannel condenser and returnthe refrigerant to the HVAC system.
 4. The HVAC system of claim 1further comprising a solenoid valve, the solenoid valve operable to beopened by the controller and to allow refrigerant to enter the bypassline.
 5. The HVAC system of claim 1 further comprising a second pressuresensor.
 6. The HVAC system of claim 1 further comprising a distributor.7. The HVAC system of claim 1 wherein the pressure sensor is locatedproximate the outlet of the condenser.
 8. The HVAC system of claim 3wherein the second bypass line comprises a solenoid valve.
 9. A methodof relieving pressure within an HVAC system comprising: receiving asignal to start the HVAC system; opening a bypass line, the bypass linecapable of diverting refrigerant away from an expansion valve andreturning the refrigerant to the HVAC system; starting the HVAC system;and closing the bypass line when a predetermined event has occurred. 10.The method of claim 9 wherein the predetermined event is a period oftime.
 11. The method of claim 9 wherein the predetermined event is apredetermined pressure threshold.
 12. The method of claim 9 wherein theHVAC system comprises a microchannel condenser.
 13. The method of claim9 wherein the bypass line comprises a pressure regulating valve.
 14. Themethod of claim 9 wherein the bypass line comprises a solenoid valve.15. The method of claim 9 wherein the HVAC system comprises adistributor.
 16. The method of claim 9 further comprising providing asecond bypass line that directs refrigerant away from the condenser andreturns the refrigerant to the HVAC system.
 17. A method of operating anHVAC system comprising a controller, a condenser, a compressor, anevaporator, and an expansion device, the method comprising: receiving,at the controller, a pressure reading for the HVAC system; opening, bythe controller, a valve to a bypass line when the pressure readingexceeds a predetermined value; wherein the bypass line directsrefrigerant away from an expansion device and returns the refrigerant tothe HVAC system.
 18. The method of claim 17 further comprising closingthe valve to the bypass line when an event has occurred.
 19. The methodof claim 17 the HVAC system comprises a microchannel condenser.
 20. Themethod of claim 17 wherein the HVAC system comprises a fin tubeevaporator.